Multiband metamaterial microwave absorbers using split ring and multiwidth slot structure

This article proposes a multiband metamaterial microwave absorber based on a split ring-slot structure. Both simulation and experimental measurements are carried out to obtain the scattering parameters which are used to retrieve the absorption coefficient, relative permittivity, and relative permeability. The influences on the absorption produced by geometrical dimensions, incidence angles and polarisation angles are investigated from 1.5 to 18.0 GHz. The results show that the absorber possesses three resonance peaks with absorption greater than 70% measured experimentally at 3.0, 5.8, and 11.0 GHz. The absorption performance is insensitive to the angle of incidence, θ up to 60�.The absorption mechanisms are studied based on the surface current distribution, electric field distribution, and constitutive parameters (μr and εr). Furthermore, a mechanical mean using dielectric material to tune the absorption frequencies (up to 1.0 GHz of tuning range) and enhance the absorption bandwidth (up to 50%) is demonstrated

Significance of Speech Intelligibility Assessors in Medium Classroom Using Analytical Hierarchy Process

When there are constraints on the resources-equipment, manpower and time-to conduct speech intelligibility tests, the most reliable or significant SI assessor for many different types of rooms is always sought for. The purpose of this study was to determine the most significant speech intelligibility assessor in four medium classrooms. The speech intelligibility assessors tested were RT60, C50, D50, and STIPA. The data were acquired by means of sound recorder that recorded six Malay words spoken by a trained male speaker, in four medium classrooms.The recorded speech signals were analyzed by DIRAC software. The data of four speech intelligibility assessors have to be normalized before it can be analyzed by AHP. In conclusion, C50 has shown the most consistent prediction of speech intelligibility in all sampled classrooms. On the other hand, as the room gets larger, RT60 becomes significant for determining speech intelligibility in these sampled classrooms

Miniaturization of three-section branch-line coupler using diamond-series stubs microstrip line

A three-section branch-line coupler is miniaturized using diamond-series stubs microstrip lines. The modified coupler is capable of operating from 1.6GHz to 3GHz with a return loss of less than −20 dB, phase imbalance of less than 2.5°, insertion loss and coupling of −4.5±1.5 dB and −2.5±0.5 dB, respectively over the operating range. The bandwidth of the coupler has been extended up to 1.4GHz. In addition, it achieves up to 83.3% size reduction as compared to the conventional three-section coupler. Furthermore, its performance and circuit size are compared with another modified coupler with normal open-stubs microstrip lines. Significantly, this study focuses on analyzing and discussing the effects of diamond structure and number of stubs. Furthermore, the achieved results are superior to the previous studies

The study of normal incidence sound absorption coefficience (Sound Absorption) of wood circular perforated panel (CPP) using numerical modelling technique

Wood Circular Perforated Panel (WCPP) is the simple form of direct piercing carved wood panel (DPCWP) which has been widely used in traditional and modern mosques as part of wall partition. This DPCWP can act as sound absorption material. Normal incidence sound absorption coefficient (αn) of WCPP can not be tested using conventional sound absorption measurement techniques. Nowadays, numerical modeling is a powerful technique to solve these difficulties. Numerical modeling based on Boundary Element Method (BEM) has been widely used for engineering design and prediction. This thesis report on work that has been carried out to investigate normal incidence sound absorption coefficient, (αn) characteristics of wood circular perforated panel (WCPP) using Boundary Element Method. The perforation ratios investigated are 20%, 30% and 40 %. The panel perforation ratio is ranging in number of apertures, diameter, and distance between apertures. Boundary Element Method simulation is done using Beasy Acoustics software. The simulation is done by creating WCPP geometric model, defining acoustics media properties and boundary conditions. Net sound intensity is simulated by creating point source 2 meter in front of the panel and 16 internal points 0.25λ in front of the panel. Incidence sound intensity is obtained by removing the panel. Comparison and analysis of αn of WCPP modeled by BEM with αn measured using sound intensity technique and theoretical prediction were conducted. It was found out that there is a close correlation of αn modeled using BEM and αn measured using sound intensity and theoretical prediction. Statistical regression model for simulation result is developed using SPSS. Third order polynomial is applied to fit the curves of WCPP simulation result and multiple regression model with stepwise method is applied to fit the curve of over all result with perforation ratio and frequency band as independent variable

Theoretical modelling of normal incidence sounds absorption coefficient of wood circular perforated panel due to resonance frequency

Wood Perforated Panels (WPP) has been used as part of wall partition of an enclosed room particularly in mosques. Wood Circular Perforated Panels (WCPP) is the simplest form of WPP. Due to non-existence of reliable normal incidence sound absorption coefficient ( n ï?¡ ) for WCPP, the consideration of WCPP as a sound absorption material cannot be ignored. It is believe that the WCPP can act as sound absorption material as it has inherent capability to allow sound waves to pass through easily. This research investigate the normal incidence sound absorption coefficient ( n ï?¡ ) of WCPP due to resonance frequencies using numerical modelling technique. The numerical experiments are conducted using Boundary Element Method (BEM) since it is a powerful computational method. It is among the most recent tool and providing numerical solutions for Acoustic Engineering design. The complexity of the design and simulation of WCPP is then resolved using quarter modelling technique. The perforation ratios investigated are 30% and 40%. The aperture creation begins with the calculation of aperture dimension. This dimension was calculated to resonate at 1 kHz, 2 kHz and 4 kHz with n = 1, 2 and 3. Then it is followed by modeling and compilation process for room with WCPP and empty room. n ï?¡ of WCPP due to resonance frequencies was calculated by dividing net sound intensity value in front of the circular panel with incident sound intensity obtained in empty room. From the numerical simulation result, it was found that n ï?¡ from 250 Hz to 500 Hz is mainly due to mass transfer. Whereas, from 2 kHz to 4 kHz, the n ï?¡ are contributed by its resonance frequency. At 1 kHz, it is shown that n ï?¡ value is in the transition state, between mass transfer and resonance frequency effect. The electroacoustics calculation of R,L,C of WCPP at 30 % and 40 % perforation ratio also shown that the RLC values are reasonably small and shall not affect to the n ï?¡ significantly

Normal incidence sound absorption coefficient of direct piercing carved wood panels (DPCWP) with geometric pattern

Direct piercing carved wood panels (DPCWP) have been used as part of the wall panel for mosques in this country. Among the earliest used of DPCWP is as in Masjid Sultan Zainal Abidin in 1700s, Kuala Terengganu, Terengganu. Among the most recent used of the DPCWP in modern mosque is as in Masjid Putrajaya, Putrajaya, Wilayah Persekutuan. In the case of Masjid Sultan Zainal Abidin, it is envisage, the use of DPCWP is to help in achieving good speech intelligibility inside. This is considering DPCWP allowing sound waves to pass through, hence sound reflection to the main prayer is contain. Minimizing sound reflection toward the mosque main area, ensuring optimization of speech intelligibility. However the use of DPCWP with geometric pattern in Masjid Putrajaya is foresee mainly due to esthetic consideration. This is considering wood carving is among the identity for Malay architecture. The property of DPCWP to allow sound waves to pass through qualifies DPCWP as sound absorber material. This as Sabine, Kutruff and Maekawa definition of sound absorption coefficient. In this research work, the DPCWP with various geometric patterns in the region of 25% to 40% perforation ratio was investigated. Numerical experiments were conducted using Boundary Element Method (BEM). The measured results were obtained using sound intensity measurements technique. Analysis results of sound absorption coefficient for both techniques were discussed using graph and table arrangement. Analysis of resonance frequencies due to types and sizes of apertures in relation to sound absorption coefficient also be highlighted. The measured and numerical results suggest, DPCWP with geometric patterns indeed able to act as good sound absorber. This finding allows DPCWP to be used as sound absorber more effectively in future mosque construction

The reverberation time and speech transmission index of small size mosque

The need for good to excellent speech intelligibility (SI) is fundamental to the design of auditoriums, lecture halls as well as mosques since good SI is central to the function of so many enclosed room facilities. Mosques are among important infrastructure require good acoustic quality especially during Friday prayer where ‘khutbah’ is performed. Equally important is during ‘kuliah’ in order to have an intelligible speech among the congregations area. It is essential that architects should consider the acoustical properties of any enclosed room early in the design process. In practice, acoustics engineer, architects and interior design should be brought into the design team from the start preferably as early as the designing phase. It is to ensure that acoustics quality and sound reinforcement are included in infrastructure planning

The acoustics and speech intelligibility quality of Kampung Laut Mosque, Kota Bharu,Kelantan

Kampung Laut Mosque, Kota Bharu, Kelantan is of fully timber structure, built hundred years ago said to be the oldest mosque in Malaysia. The mosque currently situated at its present site in Nilam Puri, Kelantan located in Malaysia. The mosque basically is a square plan with three tier pyramid roofs. The top most is considerably high where there is a clerestory window. The acoustics and speech intelligibility quality of this mosque was analyze. The analysis of acoustics quality include mosque dimension, Reverberation Time (RT60), speech level distribution inside and speech intelligibilit quality. It is important to have good speech intelligibility as heard by congregations when 'khutbah' or sermon is performed which is very related to the RT60 of this mosque. Speech propagation analysis inside the mosque was done using ray tracing technique as well as sound pressure level analysis. Speech intelligibility is predicted based on speech propagation and acoustics analysis. Reverberation time (RT60) calculated was compared to guidelines and standard available. It was found out that Kampung Laut Mosque posses good RT60, thus good speech intelligibility. As such, this study resolved the issue that the acoustics of this mosque was really good and somehow was in the idea of this mosque's designer hundred years ago